Sack of Baghdad

The Sack of Baghdad occurred from 29 January to 10 February 1258 when the 150,000-strong Mongol army of Hulegu Khan besieged, captured, sacked, and massacred the Abbasid capital of Baghdad, killing Caliph al-Musta'sim, all 50,000 defenders, and up to 2 million civilians.

Background
The accession of Mongke Khan to the title of Great Khan in 1251 led to his brother Kublai Khan being sent to conquer China, while his brother Hulegu Khan was sent to Persia. In 1256, Hulegu entered the Middle East with over 100,000 warriors, and he conquered the remnants of the Khwarezmian empire before taking dozens of fortresses from the legendary Hashshashin order, using siege engines to destroy their forts (including Alamut). With all of Iran secured, Hulegu Khan demanded that the Abbasid caliph al-Musta'sim submit to him. al-Musta'sim refused, so, in 1258, the 150,000-strong army laid siege to Baghdad, the largest and most prosperous city in the Middle East.

Siege
al-Musta'sim sent out 20,000 cavalry to attack the Mongols, defeating the Mongol vanguard and setting up camp and feasting outside of the city. The next morning, they were caught between the Mongols on one side and the river on the other, and those who were not killed drowned. The Mongols then surrounded the city and bombarded Baghdad with siege engines, refusing to accept al-Musta'sim's surrender. On 10 February 1258, Baghdad surrendered, and it was sacked for a week, with only the Christian population being spared. The Grand Library of Baghdad was burned to the ground, ending the Islamic golden age and moving the center of the Islamic world from Baghdad to Cairo. For the first time in Muslim history, Islam was without a caliph. Up to 2 million civilians were killed during Baghdad's destruction.